<?php
// ...
if ($form->isValid()) {
    $id || $em->persist($category);
    $em->flush();
    $em->commit();

    $this->get('session')->setFlash('notice', $this->trans('changes.saved'));

    $url = $id ?
        $request->getUri() :
        $this->generateUrl('blog_admin_category_edit', array(
            'id' => $category->getId()
        ));

    return $this->redirect($url);
}
// ...